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[release/11.0] Fix IEnumerator adapter initialization for COM RCWs - #136429
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Initialize COM enumerator adapters lazily per RCW instead of during interface resolution, which cached dispatch can bypass. Reuse the existing adapter cache. Add regression coverage for repeated fresh RCWs, all three enumerator entry points, empty/nonempty collections, and reset after exhaustion. Fixes #136118 Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com> Copilot-Session: ee70b0a5-4f16-4838-9d10-fe9924d6864c
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Backport of #136392 to release/11.0
/cc @AaronRobinsonMSFT
Customer Impact
Customer-reported in #136118 on .NET 10.0.9 / Windows 11 Arm64 and reproduced locally on Windows x64. Every fresh native IEnumVARIANT RCW cast to IEnumerator should enumerate successfully. Instead, cached interface dispatch can bypass per-RCW adapter initialization after the first instance, causing NullReferenceException when using subsequent enumerators. This breaks COM collection enumeration, including Windows Firewall rules, for applications ported from .NET Framework 4.8.
Regression
Introduced by #105965 (commit 0d8e565, merged August 17, 2024), which moved RCW enumeration to IDynamicInterfaceCastable and initialized per-instance adapter state during interface resolution. That resolution can be cached without initializing later RCWs. The customer reports this worked on .NET Framework 4.8.
Testing
The new regression test reproduced the NullReferenceException without the fix and passed with it. It covers three fresh native RCWs per case, MoveNext/Reset/Current as the first member called, empty and nonempty collections, and reset after exhaustion. The existing COM Dynamic collection test did not repeatedly cast fresh native IEnumVARIANT RCWs at the same call sites.
Original main-branch validation on Windows x64 with Checked CoreCLR:
.\build.cmd clr.corelib -arch x64 -c Release -rc Checked- passed..\src\tests\build.cmd x64 Checked -Test Interop\COM\Dynamic\Dynamic.csproj -SkipNative -SkipGenerateLayout- passed using existing native test assets.CORE_ROOTset toartifacts\tests\coreclr\windows.x64.Checked\Tests\Core_Root,.\artifacts\tests\coreclr\windows.x64.Checked\Interop\COM\Dynamic\Dynamic\Dynamic.cmd- passed normally and withDOTNET_TieredCompilation=0.No additional local builds or tests were run for this backport; the local validation above was performed for the original main-branch fix.
Risk
Low. The change is limited to the Windows built-in COM IEnumerator adapter path. It lazily obtains each RCW's adapter through the existing marshaler cache instead of depending on interface-resolution side effects. There are no public API or native COM server changes. Regression coverage exercises fresh RCWs and all three enumerator members, and the existing COM Dynamic test program passed.
IMPORTANT: If this backport is for a servicing release, please verify that:
release/X.0-staging, notrelease/X.0.release/X.0(no-stagingsuffix).Package authoring no longer needed in .NET 9
IMPORTANT: Starting with .NET 9, you no longer need to edit a NuGet package's csproj to enable building and bump the version.
Keep in mind that we still need package authoring in .NET 8 and older versions.
Note
The servicing details were prepared with GitHub Copilot.